In medical and cosmetic procedures, there is a need to inject a liquid under the surface of the skin. For example, injecting insulin under the surface of the skin or injecting a substance such as collagen under the surface of the skin for cosmetic purposes is the case.
A most common method for injecting a liquid includes inserting an injection needle into a desired part to a desired depth. However, when an injection needle is used, pain and bleeding are involved, and an injection needle may be inserted improperly or wrongly based on a skill level of a user. Also, in the event of improper insertion into the skin, severe damage may occur to a skin tissue and the damaged skin needs treatment for a considerable period of time.
Accordingly, to solve the problem, a needle-free syringe has been recently developed. Examples of a needle-free syringe include U.S. Pat. No. 8,066,662, U.S. Pat. No. 7,942,845, Korean Patent No. 10-1062022, WO2010/067345, and WO2010/016049.
A needle-free syringe does not have an injection needle, and instead, ejects a liquid in the form of a high pressure microjet to allow the liquid to permeate into the skin in the form of the microjet. However, in the case of this syringe, to allow the microjet to penetrate and permeate into the skin to a desired depth, sufficient pressure and velocity needs to be guaranteed, and the microjet permeated into the skin needs to be immediately diffused into the tissue. However, the skin varies, for each layer, particularly, the stratum corneum and the epidermis, in thickness, elasticity, flexibility and hardness, and even in the same individual, varies in each part.
Thus, a needle-free syringe is very difficult to uniformly permeate a liquid, and because while permeating, an angle and a distance between a skin surface and an orifice from which a microjet is ejected and properties of a medicinal fluid to be permeated have a significant influence on an amount and a depth being permeated, controlling a loss and a permeation depth during injection of the medicinal fluid is difficult. Particularly, when a medicinal fluid of high viscosity is to be delivered, phenomena occurs in which a microjet of sufficient velocity is not generated and some of the permeated microjet is not diffused into the skin and comes out of the skin and collides backwards with a subsequent microjet emitted from an orifice, thereby further reducing the microjet velocity, resulting in further reduction in skin permeation capability.